The invention described herein may be manufactured, used or licensed by or for U.S. Government purposes without the payment of royalties thereon.
I. Field of Invention
This invention applies to the field of rail guns and more particularly, to a barrel assembly in an electromagnetic rail gun.
II. Background of the Invention.
Challenges presented by rail gun construction have existed since the early 1920s. Examples of such guns are taught in U.S. Pat. Nos. 1,370,200; 1,421,435; and 1,422,427. Current laminated-type rail gun barrels 10 for applications requiring light weight mobile use typically comprise stacked metallic annular or rectangular laminations in combination with pre-stressed tension elements to add radial and longitudinal stiffness. These laminations 11 have engineered shapes (often an elongated annular shape) to accommodate a plurality of longitudinal rails 12 within the barrel 10, and the lamination shape is optimized to contain radial forces (tending to spread the rails 12) associated with the launching of rail gun projectiles.
Longitudinal stiffness of a rail gun barrel 10 can be obtained from tension elements 13 that may be spirally wound around the barrel at a preferred angle with the barrel longitudinal axis as taught in U.S. Pat. No. 5,454,28? entitled xe2x80x9cLightweight High Lxe2x80x9d Electromagnetic Launcher.xe2x80x9d Alternatively, axial tension rods 14 may be used to preload the metallic laminates 11 in compression as shown in FIG. 1 (Prior Art), to provide a high effective bending modulus, provided the preload is not defeated by disturbance loads, Ref. xe2x80x9cA High Performance Rail Gun Launcher Design,xe2x80x9d Juston, John M. and Bauer, David P., IEEE Trans Mag., v33n1, pp. 566-570, Jan. 1997.
Radial stiffness of a rail gun barrel 10 is required in order to contain the rails 12 of the gun. In strong analogy with gas propulsion guns, the electromagnetic forces that propel the projectile out of a rail gun, also apply substantial loads to drive the rails 12 apart. The resulting strain of the rails 12 under the imposed magnetic stress may impair performance of the launcher as it propels projectiles at velocities in excess of 2/km/s. Since the rails 12 must be electrically insulated from each other, current practice is to place an insulator 15 between the two rails 12. Since it is most challenging to engineer a structure that would allow the insulator material 15 to both bind to the rails, and to provide stiffness in tension, high performance rail gun designs incorporate a substantial compressive preload of the rails 12 against the insulator 15 that separates them. Using this approach, the modulus of the insulator 15 (often a ceramic), may contribute to reducing the dynamic strains of the rails 12 during operation, as long as the stresses do not exceed the preload magnitude. This is in complete analogy with any engineered tension compression system including tires and pre-stressed concrete.
Two methods of achieving this desirable pre-stress are depicted in FIGS. 2A (PRIOR ART) and 2B (PRIOR ART). In FIG. 2A (PRIOR ART), a wedge 16 is driven between a split insulator 15 after the rail gun assembly has been undertaken. In FIG. 2B (PRIOR ART), a xe2x80x9cflatjackxe2x80x9d 18 is assembled between the main rails 12 and outer tensile containments structure 11. After assembly, the xe2x80x9cflatjackxe2x80x9d 18 is pressurized with epoxy driving the rails 12 inward against the insulator (ceramic sidewall 19) while pulling the composite overwrap 20 out in tension. The epoxy subsequently cures to a solid state, making the pre-stress permanent.
Active cooling channels 21 are also generally required for heat dissipation in rail guns due to the very high ohmic heat loss effects which are on the order of twenty times more heat input to the launcher than a traditional gas gun. Thus active cooling channels 21 are desirable. In the design shown in FIG. 2B, active cooling channels 21 are integrated directly with the conducting rails 12, see xe2x80x9cCannon-Caliber Electromagnetic Launcher, xe2x80x9d Zielinski, Alex E. and Werst, M. D. . IEEE Trans Mag, v33n1, pp. 630-635, Jan. 1997. With the design shown in FIG. 2A, conduction of the heat from the rails 12 through the containment structure 11 is sought to later dissipate the heat to the environment through the outer layer of the barrel 10. Both of these approaches have limited success due to the fact of the small heat capacity of the surrounding air, and the low surface area of the outer skin of these types of rail designs.
To date, there is a need in this art for robust structural components in a rail gun, wherein these components can be preloaded to provide adequate pre-stressing of the containment structure for applications requiring light-weight mobile use.
Accordingly, it is an object of this invention to provide an improved containment barrel for a rail gun that enables increased muzzle energy and accuracy of a projectile.
Another object of this invention is to provide a design for a rail gun, wherein the barrel incorporates desired preload stresses in the gun containment structures.
Another object is to provide a design for a rail gun, wherein location of the cooling channels are in an area of low structural strain to provide active cooling of the rail gun, yet impart minimal impact to a rail gun design.
Finally another object of this invention is to substantially overcome the shortcomings in prior rail gun barrels and methods for making them, relating particularly to rail guns which are sufficiently strong, lightweight and stiff for mobile applications.
It has now been discovered that the above and other objects of the present invention may be accomplished by the following mechanism and in the following manner.
The rail gun barrel of the present invention comprises a pair of elongated, generally parallel conductive rails extending along opposite sides of the bore and being symmetrical about a longitudinal axis of the bore; a pair of elongated insulators disposed generally coextensively with the rails and circumferentially between them and maintained in a compressed state; a circumferential sleeve surrounding the insulators; a plurality of Belleville containment disks maintained in a stack that are compressed and surround the circumferential sleeve, each containment disk having a substantially hollow form with an outer surface, and an inner surface; and a plurality of longitudinal tension rods, disposed substantially parallel to the longitudinal axis of the bore and disposed external to the sleeve, the tension rods compresses the plurality of Belville containment disks.